Seamless steel pipe for oil wells excellent in sulfide stress cracking resistance and method for producing the same

Abstract

A high-strength seamless steel pipe for oil wells excellent in sulfide stress cracking resistance which comprises, on the percent by mass basis, C: 0.1 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.05 to 1.0%, Cr: 0.05 to 1.5%, Mo: 0.05 to 1.0%, Al: 0.10% or less, Ti: 0.002 to 0.05% and B: 0.0003 to 0.005%, with a value of equation “C+(Mn / 6)+(Cr / 5)+(Mo / 3)” of 0.43 or more, with the balance being Fe and impurities, and in the impurities P: 0.025% or less, S: 0.010% or less and N: 0.007% or less. The seamless steel pipe may contain a specified amount of one or more element(s) of V and Nb, and / or a specified amount of one or more element(s) of Ca, Mg and REM. The seamless steel pipe can be produced at a low cost by adapting an in-line tube making and heat treatment process having a high production efficiency since a reheating treatment for refinement of grains is not required.

Description

[0001] This application is a continuation of the international application PCT / JP2005 / 001186 filed on Jan. 28, 2005, the entire content of which is herein incorporated by reference.TECHNICAL FIELD [0002] The present invention relates to a high strength seamless steel pipe which is excellent in sulfide stress cracking resistance and a method for producing the same. More specifically, the present invention relates to a seamless steel pipe for oil wells having a high yield ratio and also excellent sulfide stress cracking resistance, which is produced by the method of quenching and tempering for a specified component-based steel. [0003]“An oil well” in the present specification includes “a gas well”, and so, the meaning of “for oil wells” is “for oil and / or gas wells”. BACKGROUND ART [0004] A seamless steel pipe, which is more reliable than a welded pipe, is frequently used in a sever oil well environment or high-temperature environment, and the enhancement of strength, improvement in t...

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Benefits of technology

[0011] From the point of the above-mentioned present situation, the present invention has an object to provide a high strength seamless steel pipe for oil wells having a high yield ratio and an excellent sulfide stress cracking resistance, which can be produced by an efficient means capable of realizing an energy saving. MEAN FOR SOLVING THE PROBLEMS

Problems solved by technology

Accordingly, the sulfide stress cracking resistance is generally deteriorated against the enhancement in strength of the steel product used in a hydrogen sulfide-rich environment.

Although it is preferable to make the steel product into a uniform tempered martensitic microstructure for increasing the yield ratio of the steel, that alone is insufficient.

However, the refinement of austenite grains needs quenching in an off-line heat treatment, which deteriorates the production efficiency and increases the energy used.

Therefore, this method is disadvantageous in these days where rationalization of cost, improvement in production efficiency and energy saving are indispensable to manufacturers.

However, such measures have the difficulties as described above.

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